Lock-up control device for torque converter in automatic transmission for vehicle

ABSTRACT

In an automatic transmission for a vehicle, a lock-up device is provided for a direct coupling clutch. The automatic transmission includes a fluid type torque converter having a hydraulic direct coupling clutch, and an auxiliary transmission having plural stages of gear trains. The lock-up control device has a valve for controlling the supply of oil pressure from a common oil pressure source to the direct coupling clutch, the valve having a body movable between opposite end positions and adapted to take a first switch position at one of the end positions when applied with a single signal pressure and a second switch position at the other end position, after release of the signal pressure, due to resilient force of a spring. The valve allows flow of the actuating oil pressure to the direct coupling clutch when the valve body is at both the first and second switch positions and interrupts the flow during shifting movement of the valve body from the first to second positions or vice versa. Thus, the direct coupling clutch is instantaneously disconnected during gear shifting operation over adjacent three gear ratios with use of the single signal pressure.

This is a division, of application Ser. No. 551,739 filed Nov. 14, 1983now U.S. Pat. No. 4,589,537.

BACKGROUND OF THE INVENTION

1. Field of the Invention

In an automatic transmission comprising a fluid type torque converterhaving an input member including a pump vane wheel and an output memberincluding a turbine wheel, and an auxiliary transmission having one ormore stages of gear trains, through which the torque of the outputmember is transmitted to a driving wheel, a lock-up control device for atorque converter in which a direct coupling clutch capable ofmechanically coupling said input and output members is interposedtherebetween to control the slip loss of the torque converter to theminimum.

2. Description of the Prior Art

When an accelerator pedal is released during the operation of thevehicle with the torque converter placed in a lock-up state by actuationof the direct coupling clutch, a sudden change in reaction applied to apower plant including the engine is transmitted to the vehicle bodythrough the power plant and as a consequence, unpleasant surging tendsto occur. It is effective to release the actuation of the directcoupling clutch at an idle position of an engine throttle valve in orderto avoid the unpleasant surging. Various devices for that purpose havealready been proposed.

A further means for solving this problem has already been proposed, inwhich means, a unidirectional clutch is interposed in series with thedirect coupling clutch between the input and output members of thetorque converter, said unidirectional clutch being designed so that atthe time of operation of the direct coupling clutch, only the outputtorque of the engine may be transmitted towards the output member. Inthe idle condition of the engine throttle valve, vibration noises andwear due to the slip of the unidirectional clutch somewhat occur. Ifprevention of such occurrence of the noises or the like is taken intoconsideration, it is desirable to release the direct coupling clutch.

On the other hand, the applicant has already proposed an arrangementwherein for the purpose of maintaining the power performance during theoperation of the direct coupling clutch, the slip characterisitc isimparted to the direct coupling clutch and the engaging force of thedirect coupling clutch is controlled in accordance with the change invehicle speed whereby during the maximum power output operation of theengine in a low vehicle speed zone, the slip is purposely created in thedirect coupling clutch to thereby allot the transmission of outputtorque of the engine to a mechanical transmission system including thedirect coupling clutch and a fluid transmission system including a fluidof the torque converter, thus suitably restoring a torque amplifyingfunction of the torque converter, and in other words, power division ofone kind is effected.

If an attempt is made to simultaneously effect the lock-up controls ofdifferent kinds, two valves are required, one valve for releasing thedirect coupling clutch in the idle state of the engine throttle valveand the other for controlling the coupling force of the direct couplingclutch in accordance with the change in vehicle speed. If these can becontrolled efficiently by a single valve, the device is materiallysimplified, and a leak loss of pressure oil from the valve is minimized,which is extremely advantageous in practical use.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide alock-up control device for said torque converter which is simple inconstruction and in which the lock-up controls of different kinds may becarried out by a single valve.

To achieve this object, the present invention is characterized bycomprising a hydraulic direct coupling clutch having a slipcharacteristic provided between input and output members of a torqueconverter and capable of mechanically coupling said both members and amodulator valve disposed in an oil passage for connecting a hydrauliccylinder of said direct coupling clutch with an oil pressure source,said modulator valve being composed of a valve body for opening andclosing said oil passage, a spring for biasing said vlave body in avalve-opening direction, a first oil pressure chamber for introducingpilot oil pressure for biasing said valve body in a valve-closingdirection from an input port side of said modulator valve, and a secondpilot oil pressure chamber for introducing pilot oil pressure forbiasing said valve body in the valve-opening direction, wherein anoutput side of a device for generating oil pressure proportional tovehicle speed for releasing oil pressure which is changed proportionalto the vehicle speed is connected through a throttle to said secondpilot oil pressure chamber and a valve device for detecting the idlestate of an engine throttle valve to release said second pilot oilpressure chamber to atmosphere is connected to said second pilot oilpressure chamber.

It is a second object of the present invention to provide a lock-upcontrol device for said torque converter which is simple in constructionand positive in operation and in which the torque converter can belocked up over three speed ratios adjacent to one another by a commoncontrol device, and at the time of speed change, said lock-up can betemporarily released to alleviate a shock at the time of speed change.

To achieve this second object, the present invention is characterized bythe provision of an automatic transmission comprising a fluid typetorque converter, a hydraulic direct coupling clutch provided betweeninput and output members and capable of being actuated to mechanicallycoupling said both members, an auxilary transmission connected to saidtorque converter and having plural stages of gear trains, said auxiliarytransmission capable of being changed in speed to a plurality of speedratios by selection of said gear trains, and a control mechanism forautomatically effecting the selection of gear trains of said auxiliarytransmission in accordance with the running condition of the vehicle,said automatic transmission comprising signal pressure which isincreased or reduced when one of said gear trains is selected so as toassume a certain speed ratio and which is conversely reduced orincreased when the other of gear trains is selected so as to assume aspeed ratio adjacent to the first-mentioned speed ratio, a lock-upactuating means for actuating said direct coupling clutch by common oilpressure even when either gear train is selected, and a release meansfor detecting a variation in said signal pressure to release the lock-upof said direct coupling clutch during a period of said variation.

Accordingly, if the oil pressure for establishing an intermediate speedstage gear train is used as a reference oil pressure of the lock-upactuating means, the actuation and relase of the direct coupling clutchcan be controlled by the oil pressure for establishing a low-speed stageand high-speed stage gear train adjacent thereto, the torque convertercan be locked up over three speed ratios, and the releasing can beeffected at the time of twice of speed change therebetween. Of course,this can be also applied to the transmission which is provided with onlytwo speed ratios.

Incidentally, where an actual control device for an automatictransmission is designed, it is advantageous, in terms of installationspace and cost, to use an output of a speed-changing governor valveheretofore used, that is, governor pressure Pg, as signal pressureproportional to the vehicle speed. However, the characteristic of thegovernor pressure Pg is generally determined by a combination of thesecondary parabola, and the rising speed of the governor pressure in alow-speed zone is high as shown in FIG. 11. This means that in thelow-speed zone, as the vehicle speed lowers, the lock-up engaging forcerapidly weakens. This is convenient because the lock-up state of thetorque converter is released before the vehicle stops to avoid theengine stop (so-called "enst"). On the other hand, however, thecharacteristic of the governor pressure Pg has its own limitation fordetermining the speed change characteristic, and the characteristic ofthe governor pressure Pg cannot be determined freely in view of the factthat the torque converter is locked up. Accordingly, if a release pointof the lock-up is brought to the lowspeed state as much as possible,there was a problem in that in the vehicle speed region above therelease point, the engaging force of the direct coupling clutch isexcessively strong to increase the vehicle vibrations. That is, in FIG.11, where the governor pressure Pg is increased to form lock-up pressurePL, if the amount of said increment is increased to PL' in order tolock-up the torque converter from a lower speed, the lock-up start pointdetermined by a point crossed with internal pressure Pc of the torqueconverter is shifted from vehicle speed A to vehicle speed B to beshifted to the lower speed side. However, in vehicle speed C which isthe middle-speed zone, the engaging force of the torque converterincreases and therefore, the vehicle vibration increases and poor powerfeeling results.

It is therefore a third object of the present invention to provide alock-up control device for said torque converter which can considerablyimprove practical fuel cost without making sacrifices for others whilesolving the problem of vibration in the middle-speed zone and being madeto be able to maintain the lock-up engaging force down to the low-speedzone, under the restriction that the existing speed-changing governorpressure is utilized.

To achieve this third object, the present invention is characterized bythe provision of an automatic transmission comprising a fluid typetorque converter having an input member and an output member to whichthe output of the engine is transmitted; a hydraulic direct couplingclutch provided between said input and output members and capable ofbeing actuated to mechanically engage said both members; an auxiliarytransmission connected to the output member of said torque converter andhaving plural stages of gear trains, said auxiliary transmission capableof being changed in speed to a plurality of speed ratios by selection ofsaid gear trains; and a control mechanism having a governor valve forreleasing governor pressure proportional to the vehicle speed andautomatically selecting the gear train of said auxiliary transmission inaccordance with the running condition of the vehicle; said automatictransmission comprising an oil pressure generating means for generatingoil pressure at a substantially given level at all times during theoperation of the engine; and a selection means for comparing thegovernor pressure from said governor valve with the generated oilpressure of said oil pressure generating means to select higher one ofoil pressure, output pressure of said selection means being used as anindex for controlling the engaging force of said direct coupling clutch.

Where the lock-up engaging force is made to be maintained down to alower speed zone in accordance with the aforesaid third object, if saidsystem is applied even to the speed change ratio (the first speed) ofthe low-speed stage, a switching valve for releasing the lock-up statebecomes necessary in a level below a certain vehicle speed. Otherwise,the locking-up of the torque converter is effected even during thestoppage of the vehicle, and therefore, the engine is not operatedsmoothly and for the worst, the engine stop possibly occurs (in case ofthe power divison type, the engine stop does not always occurcompletely).

It is therefore a fourth object of the present invention to provide alock-up control device for said torque converter in which in the stateof speed change ratio of a low-speed stage, pressure with the governorpressure increased is used as the lock-up engaging pressure, and thecharacteristic wherein said governor pressure rapidly lowers as thevehicle speed lowers is utilized, whereby possible occurrence of theengine stop is eliminated even in the low-speed stage and the torqueconverter can be locked up without newly installing an exclusive-useswitching valve which changes in switching mode in accordance with thevehicle speed.

To achieve this fourth object, the present invention is characterized bythe provision of an automatic transmission comprising a fluid typetorque converter having an input member and an output member to whichthe output of the engine is transmitted; a hydraulic direct couplingclutch provided between said input and output members and capable ofbeing actuated to mechanically engage said both members; an auxiliarytransmission connected to the output member of said torque converter andhaving plural stages of gear trains, said auxiliary transmission capableof being changed in speed to a plurality of speed ratios by selection ofsaid gear trains; and a control mechanism having a governor valve forreleasing governor pressure proportional to the vehicle speed andautomatically selecting the gear train of said auxiliary transmission inaccordance with the running condition of the vehicle; said automatictransmission comprising an oil pressure generating means for generatingoil pressure at a substantially given level at all times during theoperation of the engine; a selection means for comparing the governorpressure from said governor valve with the generated oil pressure ofsaid oil pressure generating means to select higher one of oil pressure;and an interruption means interposed between said selection means andsaid oil pressure generating means to cut-off a connection between saidselection means and said oil pressure generating means when the speedratio of the low-speed stage is established, output pressure of saidselection means being used as an index for controlling the engagingforce of said direct coupling clutch.

The above and other objects, characteristics and advantages of thepresent invention will be further apparent from the description ofpreferred embodiments which will be explained in detail with referenceto the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 show a first embodiment of the present invention, in whichFIG. 1 is a schematic view as a whole of a transmission for anautomobile with three stages of forward movement and one stage ofbackward movement, FIG. 2 is an oil pressure control circuit view ofsaid automatic transmission including the device of the presentinvention, FIG. 2A is a developed view showing essential parts of adirect coupling clutch of FIG. 2, FIG. 3 is a characteristic curve ofworking oil pressure of the direct coupling clutch, FIG. 4 is a viewshowing the relation between the speed change characteristic and thezones showing the strength of the engaging force of the direct couplingcluch;

FIG. 5 is an oil pressure circuit view showing a second embodiment ofthe present invention;

FIG. 6 is an oil pressure circuit view showing a third embodiment of thepresent invention;

FIGS. 7 A-D are explanatory views showing the operation of a timingvalve in FIG. 6 in order;

FIG. 8 is a characteristic curve showing the change in working oilpressure of the direct coupling cluch in FIG. 6 when the speed change ismade;

FIG. 9 is an oil pressure circuit view showing a fourth embodiment ofthe present invention;

FIG. 10 is an oil pressure circuit view showing a fifth embodiment ofthe present invention;

FIG. 11 is an oil pressure characteristic curve for explanation ofproblems;

FIG. 12 is an oil pressure circuit view showing a sixth embodiment ofthe present invention;

FIG. 13 is a curve showing the engaging pressure of the direct couplingclutch in FIG. 12;

FIG. 14 is a view for explanation of a zone capable of engaged drivingof the direct coupling clutch;

FIG. 15 is an oil pressure circuit view showing essential parts in amodified example of the timing valve in FIG. 12; and

FIGS. 16, 17 and 18 are oil pressure circuit views showing essentialparts of a seventh embodiment, an eigth embodiment and a ninthembodiment, respectively, of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present will be described indetail with reference to the accompanying drawings.

Prior to the explanation of a first embodiment of the present invention,FIG. 1 is a schematic view of an automatic transmission for a vehiclewith three stages of forward movement and one stage of backward movementto which the present invention is applied. Referring to FIG. 1, theoutput of the engine E is transmitted, via a torque converter T, anauxiliary transmission M and a differential device Df in said order,from a crank shaft 1 to driving wheels W, W' to drive the latter.

The torque converter T comprises a pump vane wheel 2 connected to thecrank shaft 1, a turbine vane wheel 3 connected to an input shaft 5 ofthe auxiliary transmission M, and a stator vane wheel 4 connectedthrough a unidirectional clutch 7 to a stator shaft 4a relativelyrotatably supported on the input shaft 5. The torque transmitted fromthe crank shaft 1 to the pump vane wheel 2 is transmitted to the turbinevane wheel 3 hydrodynamically, and when amplifying action of torque iseffected during that period, the stator vane wheel 4 bears the reactionthereof.

A pump driving gear 8 for driving an oil pressure pump P shown in FIG. 2is provided on the right end of the pump vane wheel 2, and a stator arm4b for controlling a regulator valve Vr shown in FIG. 2 is fixedlymounted on the right end of the stator shaft 4a.

Between the pump vane wheel 2 and the turbine vane wheel 3 is provided aroller type direct coupling clutch Cd capable of mechanically couplingthe former. This will be described in detail with reference to FIG. 2and FIG. 2A. An annular driving member 10 having a driving conicalsurface 9 in the inner circumference thereof is secured to the innercircumferential wall 2a of the pump vane wheel 2. A driven member 12having a driven conical surface 11 parallel to and facing to saiddriving conical surface 9 in the outer circumference thereof is axiallyslidably spline-fitted in the inner circumferential wall 3a of theturbine vane wheel 3. The driven member 12 is formed at its one endintegrally with a piston 13. The piston 13 is fitted into a oil pressurecylinder 14 provided on the inner circumferential wall 3a of the turbinevane wheel 3 to simultaneously receive internal pressure of the cylinder14 and internal pressure of the torque converter T at both left andright ends thereof.

A columnar clutch roller 15 is interposed between the driving and drivenconical surfaces 9, 11. The clutch roller 15 is retained by an annularretainer 16 in such a manner than the center axis o thereof is inclinedby a fixed angle θ with respect to the cetner line g of a phantomconical surface Ic extending through the central portion between boththe conical surfaces 9 and 11, as shown in FIG. 2A.

Accordingly, when oil pressure higher than internal pressure of thetorque converter T is introduced into the oil pressure cylinder 14 atthe stage wherein the torque amplifying function of the torque converterT becomes unnecessary, the piston 13, namely, the driven member 12 isurged towards the driving member 10. Thereby the clutch roller 15 ispressed against both the conical surfaces 9, 11 but when the drivingmember 10 is rotated by the output torque of the engine E in a directionas indicated by X in FIG. 2A with respect to the driven member 12, theclutch roller 15 revolves accordingly. However, this clutch roller 15has its center axis inclined as previously mentioned, and therefore,said revolution imparts both the members 10, 12 a relative axialdisplacement to move them close to each other. As a consequence, theclutch roller 15 is cut into and between both the conical surfaces 9, 11to mechanically couple between both members 10, 12, that is, between thepump vane wheel 2 and turbine vane wheel 3. If the output torque of theengine above the coupling force is applied between both the vane wheels2, 3 even when the direct coupling clutch Cd is operated as describedabove, the clutch roller 15 produces a slip with respect to each of theconical surfaces 9, 11. Thereby said torque is divided into two parts,one torque being transmitted mechanically through the direct couplingclutch Cd, the other being transmitted hydrodynamically through both thevane wheels 2, 3, to form a variable rate power divisional systemwherein the ratio of the former torque to the latter torque varies witha slip degree of the clutch roller 15.

When a reverse load is applied to the torque converter T during theoperation of the direct coupling clutch Cd, the rotational speed of thedriven member 12 exceeds the rotational speed of the driving member 10,and therefore, relatively, the driving member 10 is rotated in adirection as indicated by Y with respect to the driven member 12, as aconsequence of which the clutch roller 15 revolves in a directionopposite the former to impart both the members 10, 12 a relative axialdisplacement for moving them apart from each other. As a result, theclutch roller 15 is released from its cutting into and between both theconical surfaces 9, 11, assuming the idle state. Thus, the transmissionof the reverse load from the turbine vane wheel 3 to the pump vane wheel2 is effected only hydrodynamically.

If the oil pressure of the oil pressure cylinder 14 is released, thepiston 13 receives the internal pressure of the torque converter T andthen moves back to its original position, whereby the direct couplingclutch Cd assumes an inoperative state.

Turning again to FIG. 1, a low-speed stage gear train G₁, a middle-speedstage gear train G₂, a high-speed stage gear train G₃ and aback-movement gear train Gr are provided in parallel between the inputand output shafts 5, 6 parallel to each other of the auxiliarytransmission M. The low-speed stage gear train G₁ comprises a drivinggear 17 connected to the input shaft 5 through a low-speed stage clutchC₁ and a driven gear 18 connected to the output shaft 6 through aunidirectional clutch Co and meshed with said gear 17. The middle-speedstage gear train G₂ comprises a driving gear 19 connected to the inputshaft 5 through a middle-speed stage clutch C₂ and a driven gear 20connected to the output shaft 6 through a switching clutch Cs and meshedwith said gear 19. The high-speed stage gear train G₃ comprises adriving gear 21 fixedly mounted on the input shaft 5 and a driven gear22 connected to the output shaft 6 through a high-speed stage clutch C₃.The backward-movement gear train Gr comprises a driving gear 23 fromedintegrally with the driving gear 19 of the middle-speed stage gear trainG₂, a driven gear 24 connected to the output shaft 6 through theswitching clutch Cs and an idle gear 25 meshed with both the gears 23,24. The switching clutch Cs is disposed between the driven gears 20, 24,and the driven gears 20, 24 can be selectively connected to the outputshaft 6 by shifting a selector sleeve 26 of the clutch Cs to a forwardposition on the lefthand or to a backward-movement position on therighthand in the figure.

If only the low-speed stage clutch C₁ is engaged when the selectorsleeve 26 is retained at the forward position as shown, the driving gear17 is connected to the input shaft 5 to establish the low-speed stagegear train G₁, through which gear train G₁, the torque is transmittedfrom the input shaft 5 to the output shaft 6. Next, when themiddle-speed stage clutch C₂ is engaged while the low-speed stage clutchC₁ remains engaged, the driving gear 19 is connected to the input shaft5 to establish the middle-speed stage gear train G₂, through which geartrain G₂, the torque is transmitted from the input shaft 5 to the outputshaft 6. During that period, the output shaft 6 rotates at a higherspeed than that of the driven gear 18 of the low-speed train G₁ due to adifference in change gear ratio between the low-speed and middle-speedstage gear trains G₁, G₂, and therefore, the unidirectional clutch Coslips to render the low-speed stage gear train G₁ substantially out ofoperation. If the middle-speed stage clutch C₂ is interrupted andhigh-speed stage clutch C₃ is engaged while the low-speed stage clutchC₁ is engaged, the driven gear 22 is connected to the output shaft 6 toestablish the high-speed stage gear train G₃, through which gear trainG₃, the torque is transmitted from the input shaft 5 to the output shaft6. Also in this case, the unidirectional clutch Co slips to render thelow-speed stage gear train G₁ out of operation, similar to the time whenthe middle-speed stage gear train G₂ is established. Next, if theselector sleeve 26 is switched to the backward-movement position on therighthand and only the middle-speed stage clutch C₂ is engaged, thedriving gear 23 and driven gear 24 are connected to the input shaft 5and output shaft 6, respectively to establish the backward-movement geartrain Gr, through which gear train Gr, the torque is transmitted fromthe input shaft 5 to the output shaft 6.

The torque transmitted to the output shaft 6 is transmitted from anoutput gear 27 provided on the end of said shaft 6 to a large-diametergear 28 of the differential device Df.

FIG. 2 shows a combination of one example of an oil pressure circuit forcontrolling the operation of the low-speed, middle-speed and high-speedstage clutches C₁, C₂ and C₃ in FIG. 1 and one example of a controldevice Dc of the direct coupling clutch Cd in accordance with thepresent invention. In the figure, the oil pressure pump P sucks the oilfrom an oil tank R and feeds the oil under pressure into an operatingoil passage 29. This pressure oil is regulated in pressure to apredetermined level by a regulator valve Vr, and thereafter fed to amanual valve Vm. This oil pressure is termed as the line pressure Pl.

The regulator valve Vr has a pressure regulating spring 30 and a springreceiving cylinder 31 for carrying an outer end thereof, and this springreceiving cylinder 31 can be moved to left and right to adjust the setload of the pressure regulating spring 30. The stator arm 4b comes intocontact with the outer surface of the spring receiving cylinder 31 so asto apply the reaction force acting on the stator vane wheel 4, that is,the stator reaction force thereto. A stator spring 31 for carrying thestator reaction force is connected to the spring receiving cylinder 31.Accordingly, if the stator reaction force increases, the stator spring32 is compressed, as a consequence of which the spring receivingcylinder 31 is moved leftwards to increase the set load of the pressureregulating spring 30 with the result that the oil pressure of theoperating oil passage 29 is increased.

A part of pressure oil regulated by the regulator valve Vr is introducedinto the torque converter T via an inlet oil passage 34 having athrottle 33 to pressurize the interior thereof to prevent a cavitation,said internal pressure being determined by the magnitude of the throttle33, the string of a spring 37 of a check valve 36 provided on an outletoil passage 35 of the torque converter T, and the like.

The oil having passed through the check valve 36 is returned to the oiltank R via an oil cooler not shown.

The surplus portion of pressure in discharged from the oil pressure pumpP is introduced to a lubricating oil passage 38 from the regulator valveVr and fed to various lubricating portions. A pressure regulating valve39 is connected to the lubricating oil passage 38 in order to secure theoil pressure required to the minimum.

When the valve Vm is in a neutral position N as shown, the pressure oilfed to the manual valve Vm is not fed to any of said clutches C₁, C₂, C₃and various other oil pressure operating portions. When the valve Vm ismoved leftwards by one step from the illustrated position and shifted toa drive position D, the operating oil passage 29 from the oil pressurepump P is communicated with an operating oil passage 41₁ leading to anoil pressure cylinder 40₁ of the low-speed stage clutch C₁ and with anoperating oil passage 43 leading to a spring chamber 42 of an oilpressure servo-motor Sm for shifting the selector sleeve 26, andtherefore, the low-speed stage clutch C₁ is actuated (engaged) toestablish the low-speed stage gear train G₁. And a piston 44 of theservo-motor Sm remains at a positiom moved leftwards as shown to holdthe selector sleeve 26 at the forward position as shown in FIG. 1through a shift fork 45 thereby placing the backward-movement gear trainGr in an inoperative state.

An inlet oil passage 46 in communication with an input port of a devicefor generating oil pressure proportional to vehicle speed, that is, agovernor valve Vg is branched from the operating oil passage 43 leadingto the spring chamber 42 of the servo-motor Sm, and a first signal oilpassage 47₁ extends from an output port of the valve Vg.

The governor valve Vg, which is well known, is rotated about arotational shaft 49 by a gear 48 meshed with the large-diameter gear 28of the differential device Df. Thus, the rotational speed is proportionto the vehicle speed, and therefore, the governor valve Vg can releasethe oil pressure proportional to the vehicle speed, that is, a governorpressure Pg, to the first signal oil passage 47₁ by the action of thecentrifugal force acting on a weight 51 of a spool valve body 50.

An inlet oil passage 53 in communication with an input port of athrottle valve Vt is branched from the operating oil passage 43, and asecond signal oil passage 47₂ extends from an output port of the valveVt. A modulator valve 54 for determining an upper limit value of theinlet pressure of the throttle valve Vt is disposed halfway of the inletoil passage 53.

The throttle valve Vt, which is well known, comprises a spool valve body55, a control spring 58 for biasing the valve body 55 leftwards, areturn spring 57 for biasing the valve body 55 rightwards, a controlspring 59 for carrying the outer end of the control spring 58, a controlcam 60 rotated in association with an increase in opening degree of thethrottle valve of the engine E to move the control piston 59 leftwards,an adjusting bolt 61 capable of adjusting the set load of the returnspring 57 and the like. When the control piston 59 is moved leftwards,the displacement thereof causes the spool valve body 55 to be pushedleftwards through the control spring 58. With this leftward movement,the oil pressure released to the second signal oil passage 47₂ acts on aleft shoulder 55a of the spool valve body 55 so as to push back thespool valve body 55 rightwards, and therefore, after all, the throttlevalve Vt can release the oil pressure proportional to the opening degreeof the throttle valve of the engine E, that is, throttle pressure Pt, tothe second signal oil passage 47₂.

The first and second signal oil passages 47₁, 47₂ are connected to pilotoil pressure chambers 62, 62'; 63, 63', respectively, on both ends of alow-middle speed shift valve V₁ and a middle-high speed shift valve V₂.Thereby, spool valve bodies 64, 65 of these shift valves V₁, V₂ receiveat both end surfaces thereof said governor pressure Pg and throttlepressure Pt and are operated as follows:

That is, the spool valve body 64 of the low-middle speed shift valve V₁initially remains at a position moved rightwards as shown by the forceof a spring 66 but when the vehicle speed increases to increase thegovernor pressure Pg and the force for moving the spool valve body 64leftwards by the governor pressure Pg overcomes the force for moving thevalve body 64 rightwards by the throttle pressure Pt and spring 66, aclick ball 68 moving together with the valve body 64 in a click motionmechanism 67 provided on the right end of the valve body 64 gets over afixed locating projection 69 and the valve body 64 is rapidly switchedto a leftwardly moved position, whereby the oil pressure from the oilpressure pump P, which has been so far fed only to the oil pressurecylinder 40₁ of the low-speed stage clutch C₁, is also fed to the oilpressure cylinder 40₂ of the middle-speed stage clutch C₂ throughoperating oil passages 70, 71 and 41₂ to place both the clutches C₁, C₂in an engaged state, thus establishing the middle-speed stage gear trainG₂.

When the vehicle speed further increases, the similar operation occursalso in the middle-high speed shift valve V₂, whereby the spool valvebody 65 of the valve V₂ is moved leftwards due to the increasinggovernor pressure Pg to open the operating oil passages 41₂, 71 to theoil tank R and on the other hand, the operating oil passage 70 is thenbrought into communication with the operating oil passage 41₃ leading tothe oil pressure chamber 40₃ of the highspeed stage clutch C₃, andtherefore, the middle-speed stage clutch C₂ assumes the interruptedstated and the low-speed stage clutch C₁ and high-speed stage clutch C₃assume the engaged stage to establish the high-speed stage gear train G₃as previously mentioned.

Accumulators 72, 73, a unidirectional valve 74, an orifice control valve75 and the like are provided to alleviate the gear change shock.

As is well known, a gear change map divided by the solid line can bedepicted as shown in FIG. 4. Actually, the change gear map differsbetween the shift-up time and shift-down time due to the click motionmechanism 67 provided on each of the shift valves V₁, V₂. This is wellknown and is not significant. Therefore, only the map for the shift-uptime will be given.

When the manual valve Vm is shifted to a position other than the driveposition D, for example, to a middle-speed stage retaining position IIor backward-movement position Re, the middle-speed stage gear train G₂or backward-movement gear train Gr is established, which has noparticularly important relation with the present invention. No furtherexplanation will be made. Among the shift positions of the manual valveVm, a reference character Pk designates a parking position.

The aforementioned oil pressure circuit is well known.

Now, the control device Dc of the direct coupling clutch Cd will befurther explained with reference to FIG. 2. The control device Dccomprises a timing valve Tv and a modulator valve Mv.

The timing valve Tv comprises a spool valve body 80 which is movedbetween a right first switching position and a left second switchingposition, a first pilot oil pressure chamber 81 to which a left endsurface of the valve body 80 faces, a second pilot oil pressure chamber81' to which a right end surface of the valve body 80 faces, a firstinput port 83 which is always communicated with the first pilot oilpressure chamber 81 through a throttle 82 provided on the valve body 80,a second input port 83' which is always communicated with a second pilotoil pressure chamber 81' and an output port 84, wherein when the valvebody 80 is in the right first switching position, the first input port83 is placed in communication with the output port 84 and when the valvebody 80 is moved to the left second switching position, the second inputport 83+ is placed in communication with the output port 84. An oilpassage 41₂ ' branched from the operating oil passage 41₂ of themiddle-speed stage clutch C₂ is connected to the first input port 83,and an oil passage 42₃ ' branched from the operating oil passage 41₃ ofthe high-speed stage clutch C₃ is connected to the second input port83', the output port 84 being connected to the later-appearing inputport 89 of the modulator valve Mv through an output oil passage 85.

The modulator valve Mv comprises a spool valve body 86 which is movedbetween a right closed position and a left open position, a spring 87for biasing the valve body 86 towards the open position, a first pilotoil pressure chamber 88 which a left end surface of the valve body 86faces, a second pilot oil pressure chamber 88' to which a right endsurface of the valve body 86 faces, an input and output ports 89, 90,the output port 90 being connected to the oil pressure cylinder 14 ofthe direct coupling clutch Cd through an output oil passage 91. Thefirst pilot oil pressure chamber 88 is always communicated with theinput port 89 through a throttle 92 provided on the valve body 86, asignal oil passage 47₁ ' branched from the first signal oil passage 47₁is connected to the second pilot oil pressure chamber 88', and athrottle 93 is provided halfway of the oil passage 47₁ '. A dischargeoil passage 95 in communication with the oil tank R is connected to thesecond pilot oil pressure chamber 88' through a throttle 94, and anelectromagnetic valve 96 as a valve device for opening and closing thethrottle 94 is provided adjacent the modulator valve Mv. Theelectromagnetic valve 96 comprises a needle valve 97 for opening andclosing the throttle 94, a valve spring 98 for biasing the needle valve97 toward the closed side and a solenoid 99 for encircling the needlevalve 97, the solenoid 99 being connected to a power source 101 throughan idle position detecting switch 100. The idle position detectingswitch 100 is interlocked with an accelerator pedal 102 for opening andclosing the throttle valve of the engine E and the switch 100 is closedwhen the throttle valve is returned to the idle opening zone. Thethrottle 94 of the discharge oil passage 95 is set to an opening degreesmaller than the throttle 93 of the signal oil passage 47₁ '.

The operation of the control device Dc will be explained hereinafter.

First, where the vehicle is running with the establishment of thelow-speed stage gear train G₁, in this case, the low-speed stage clutchC₁ is operating, and therefore, the operating oil passages 41₂, 41₃ ofthe middle and high-speed stage clutches C₂, C₃ are communicated withthe oil tank R and thus the first and second input ports 83, 83' andoutput port 84 of the timing valve Tv and the first pilot oil pressurechamber 88 of the modulator valve Mv are also communicated with the oiltank R, and the valve body 86 of the modulator valve Mv is held in theopen position as shown by the spring force of the spring 87 and thepressing force resulting from the governor pressure Pg introduced intothe second pilot oil pressure chamber 88' through the signal oil passage47₁ ' and therefore, the interior of the oil pressure chamber 14 of thedirect coupling clutch Cd has atmospheric pressure.

On the other hand, since a part of the line pressure Pl is introudcedinto the torque converter through the throttle 33, the piston 13 of thedirect coupling clutch Cd is moved leftwards by the internal pressure ofthe torque converter T to place the clutch Cd in a released state.

When the vehicle speed increases from said condition and themiddle-speed stage clutch C₂ is actuated by being supplied with theoperating oil pressure from the operating oil passage 41₂, said oilpressure is simultaneously introduced into the first pilot oil pressurechamber 81 of the timing valve Tv via the oil passage 41₂ ' and thefirst input port 83. The valve body 80 is shifted to the right firstswitching position by said introduced oil pressure, and therefore, theoil pressure of the first input port 83 passes through the output port84, then passes through the input and output ports 89, 90 of themodulator valve Mv in the open position from the output oil passage 85and then is introduced into the oil pressure cylinder 14 of the directcoupling clutch Cd via the output oil passage 91.

At the same time, in the modulator valve Mv, the oil pressure of theinput port 89 acts even on the first pilot oil pressure chamber 88through the throttle 92, and said oil pressure imparts the rightwardlymoving force to the valve body 86. When said rightwardly moving forceovercomes the leftwardly moving force of the spring 87 and the governorpressure Pg introduced into the second pilot oil pressure chamber 88'with respect to the valve body 86, the valve body 86 is moved rightwardsso as to close the output port 90. When the relation of these forces isreversed, the valve body 86 is operated so as to open the output port90. As a consequence, the output oil pressure of the output port 90,that is, the operating oil pressure of the direct coupling clutch Cd iscontrolled from the governor pressure Pg proportional to the vehiclespeed to the modulator pressure Pm (see FIG. 3) increased to a givenlevel, said level of increment being determined by the set load of thespring 87.

Accordingly, in FIG. 3, since the modulator pressure Pm is lower thanthe internal pressure of the torque converter T at a level below thevehicle speed v₁, the direct coupling cluth Cd cannot be operated(engaged) even if the modulator pressure Pm is introduced into the oilpressure cylinder 14, thus not imparing the torque amplifying functionof the torque converter T. It can be understood from the above-describedfact that for example, in FIG. 2, even if the manual valve Vm is set tothe backward-movement position Re or the middle-speed stage retainingposition II and the middle-speed stage clutch C₂ is initially in theoperating (engaging) condition, the torque converter T is operated asusual to render possible to start the vehicle.

Also, in FIG. 3, when the vehicle speed V is in the zone of v₁ ≦v≦v₂,the modulator pressure Pm increases as the vehicle speed increases togradually strengthen the engaging force of the direct coupling clutch Cdto thereby obtain the weak engaging zone of the direct coupling clutchCd as shown by the sand-like ground in FIG. 4. Thus, when in this zone,the output torque of the engine E increases beyond the engaging force ofthe direct coupling clutch Cd, the direct coupling cluch Cd slips andthe torque of a part corresponding to the engaging force of the directcoupling clutch Cd is subject to torque amplification via a mechanicaltransmission system including the clutch Cd and the torque of a partabove the engaging force of the direct coupling clutch Cd is subject totorque amplification via a fluid transmission system including a fluidwithin the torque converter T. Therefore, after all, under the fixedvehicle speed, the power divisional driving of a variable rate whereinthe torque bearing rate of the fluid transmission system increases asthe output torque of the engine increases is effected.

When the vehicle speed V enters the high-speed zone of v>v₂, thegovernor pressure Pg introduced into the second pilot oil pressurechamber 88' of the modulator valve Mv increases enough to fully open thevalve body 86, and therefore, the modulator pressure Pm is increased upto the operating oil pressure of the middle-speed stage clutch C₂, thatis, to the line pressure Pl to augment the engaging force of the directcoupling clutch Cd to the maximum whereby the strong engaging zone ofthe direct coupling clutch Cd shown by the oblique lines in FIG. 4 isobtained. Thus, in this zone, the direct coupling clutch Cd will notslip and all the output torque of the engine E can be transmittedefficiently.

When the vehicle speed increases from said state, the operating oilpressure of the middle-speed stage clutch C₂ is released to the oil tankR and the high-speed stage clutch C₃ in place of the clutch C₂ receivesthe operating oil pressure from the operating oil passage 41₃ foroperation, that is, when the shft-up is made, said oil pressure issimultaneously introduced into the second pilot oil pressure chamber 81'of the timing valve Tv via the oil passage 41₃ ' and second input port83', and the valve body 80 is shifted to the left second switchingposition by said introduced oil pressure. However, the switchingoperation of the valve body 80 is slowly controlled by the delayedaction of the throttle 82 to impart the valve body 80 a given switchingtime. Since the operating oil pressure of the direct coupling clutch Cdis once released through the oil passage 41₂ ' already communicated withthe oil tank R during that period, the operation of the direct couplingclutch Cd is temporarily released to prevent occurrence of change gearshock.

When the valve body 80 of the timing valve Tv is shifted to the leftfirst switching position, the oil pressure of the second input port 83'is then supplied to the oil pressure cylinder 14 of the direct couplingclutch Cd through the modulator valve Mv similar to the time when themiddle-speed stage gear train G₂ is established as previously described,and the oil pressure is also controlled by the modulator valve Mv in amanner similar to that as previously described. Such an operation islikewise carried out even at the time of down-shift wherein theoperation is switched from the high-speed stage gear train G₃ to themiddle-speed stage gear train G₂.

Next, when the operating force is released from the accelerator pedal102 to decelerate the vehicle, the idle position detecting switch 100 isclosed to excite the solenoid 99 to open the needle valve 97, andtherefore, the pressure oil within the second pilot oil pressure chamber88' of the modulator valve Mv flows into the discharge oil passage 95through the throttle 94. On the other hand, the oil pressure is suppliedto the second pilot oil pressure chamber 88' through the throttle 93from the signal oil passage 47₁ '. However, the quantity of oildischarged to the discharge oil passage 95 is greater than the quantityof oil supplied to the second pilot oil pressure chamber 88' due to thedifference in size between both the throttles 93 and 94 as previouslydescribed, and after all, the pressure of the second pilot oil pressure88' assumes substantially atmospheric pressure. Thus, the modulatorvalve Mv releases the low modulator pressure Pm as indicated by thephantom outlines in FIG. 3, and since the pressure at this time is lowerthan the internal pressure of the torque converter T as indicated by thedotted lines, the direct coupling clutch Cd causes the piston 13 to bewithdrawn and is placed in a released state. For this reason, the idlezone of the opening degree of the throttle valve is shown in white inFIG. 4. In this manner, the reverse load generated with the decelerationdriving of the vehicle is transmitted hydrodynamically to the engine Ethrough the torque converter T without depending on the idle operationof the roller 15 of the direct coupling clutch Cd and therefore, thenoises and vibrations are alleviated.

FIG. 5 shows a second embodiment of the present invention. In thisembodiment, a throttle valve Vt or Vt' interlocked with the acceleratorpedal 102 is utilized as a means for releasing oil pressure from thesecond pilot oil pressure chamber 88' of the modulator valve Mv in theidle zone of the opening degree of the throttle valve. That is, anopening and closing valve 103 as a valve device which is opened when thethrottle valve Vt or Vt' is returned to the illustrated idle position isprovided on the throttle valve, and said opening and closing valve 103is incorporated in the discharge oil passage 95 branched from the signaloil passage 47₁ ' associated with the second pilot oil pressure chamber88' of the modulator valve Mv. A throttle 93 is provided on the signaloil passage 47₁ ' at an upstream from the branched portion of thedischarge oil passage 95 and a throttle 94 larger in opening degree thanthat of the throttle 93 is provided on the oil passage 95. Otherconstructions are the same as those shown in the previous embodiment. InFIG. 5, parts having the same function as that of the previousembodiment are given the same reference characters. It is noted that thethrottle 94 of the discharge oil passage 95 can be omitted.

In this manner, when the throttle valve Vt or Vt' is returned to theidle position, the opening and closing valve 103 is opened, andtherefore, the oil pressure of the second piot oil pressure chamber 88'of the modulator valve Mv is discharged to the discharge oil passage 85.Thus, the output oil pressure of the modulator valve Mv lowers similarlyto the previous embodiment and the direct coupling clutch Cd assumes areleased state.

As described above, in accordance with the present invention, a singlemodulator valve can performs two modes of lock-up control, one whereinthe engaging force of the direct coupling clutch is controlled inaccordance with the variation in vehicle speed, and the other whereinthe direct coupling clutch is released under the idle condition of theengine throttle valve. As a consequence, the present invention haseffects in that the device can be materially simplified and that a lossof leakage of pressure oil from the valve can be minimized.

FIG. 6 shows a third embodiment of the present invention. Thisembodiment is different from the previous embodiment in a timing valveTv in the lock-up control device Dc. That is, the timing valve Tvcomprises a spool valve body 80 which is moved between a right firstswitching position and a left second swtiching position, a first pilotoil pressure chamber 81 to which a left end surface of the valve body 80faces, a second pilot oil pressure chamber 81' to which a right aendsurface of the valve body 80 faces, and a spring 108 for biasing thevalve body 80 rightwards, wherein an oil passage 41₂ ' branched from anoperating oil passage 41₂ of a middle-speed stage clutch C₂ is connectedto the second pilot oil pressure chamber 81', the first pilot oilpressure chamber 81 being communicated with an oil tank R through an oilpassage 104. The valve body 80 is provided in a circumferential surfacethereof with two annular grooves 106, 107. When the valve body 80 is inthe first switching position as shown, the input oil passage 41₁ 'branched from the operating oil passage 41₁ of the low-speed stageclutch C₁ and led to the timing valve Tv is communicated with an outputoil passage 85 of the timing valve Tv through the annular groove 106,and when the valve body 80 is moved leftwards to assume the secondswitching position, the oil passage 4₁ ' is communicated with the oilpassage 85 through the annular groove 107. In the position halfwaywherein the valve body 80 is moved between the first switching positionand the second switching position, the output oil passage 85 istemporarily shut off from the input oil passage 41₁ ' and iscommunicated with the oil tank R. Other constructions are the same asthose shown in the previous embodiment. In FIG. 6, parts having the samefunction as that of the previous embodiment are given the same referencecharacters.

In this embodiment, when the vehicle speed increases and the shift valveV₁ is switched due to the difference between the governor pressure Pgand the throttle pressure Pt and the operating oil pressure is suppliedfrom the operating oil passage 41₂ in order to establish themiddle-speed stage gear train G₂ so that the middle-speed stage clutchC₂ is actuated, said oil pressure is simulataneously introduced into thesecond pilot oil pressure chamber 81' of the timing valve Tv through theoil passage 41₂ ', by which introduced oil pressure, the valve body 80is shifted to the left second switching position. The operatingconditions of the timing valve Tv during that period are shown in FIGS.7 A-D.

First, FIG. 7A shows the state similar to FIG. 6 in which the oilpressure is not applied to the second pilot oil pressure chamber 81'. Inthis case, the oil passage 41₁ ' is communicated with the oil passage 85through the annular groove 106. When the vehicle speed increases and thepressure of the oil passage 41₂ is increased by the switching operationof the shift valve V₁ or V₂, the pressure within the second pilot oilpressure chamber 81' is increased through the oil passage 41₂ '. Whenthis pressure becomes greater than the set load of a spring 108, thevalve body 80 begins to be moved leftwards and the oil passage 41, isclosed as shown in FIG. 7B. The oil passage 85 also remains closed, andthe modulator pressure Pm is maintained constant. When the pressurewithin the second pilot oil pressure chamber 81' further increases, thevalve body 80 is further moved leftwards and the oil passage 85 iscommunicated with the oil passage 104 as shown in FIG. 7C whereby thepressure oil within the oil passage 85 is circulated to the oil tank R.Thus, the modulator pressure Pm lowers and the piston 13 of the directcoupling clutch Cd is moved leftwards to releast the lock-up. When thepressure within the second pilot oil pressure chamber 81' furtherincreases and the valve body 80 is further moved leftwards, the outputoil passage 85 is shut off from the oil passage 104 as shown in FIG. 7Dand connected to the input oil passage 41₁ ' through the annular groove107. Thus, the oil pressure of the input oil passage 41₁ ' passesthrough the output oil passage 85, thence passes through the input andoutput ports 89, 90 of the modulator valve Mv in the open position, andis again introduced into the oil pressure cylinder 14 of the directcoupling clutch Cd.

FIG. 8 represents the variation of the modulator pressure Pm, that is,the engaging force of the direct copling clutch Cd, with the time tgiven by the abscissa. As will be apparent from FIG. 8, during thevariation of the oil pressure transmitted through the oil passage 41₂ ',that is, during the change gear operation, the modulator pressure Pm islower than the internal pressure Pc of the torque converter T and theoperation of the direct coupling clutch Cd is temporarily released.

When the vehicle speed increases and the middle-high speed shift valveV₂ is actuated and the high-speed stage clutch C₃ receives the operatingoil from the operating oil passage 41₃ for operation, that is, when theshift-up is effected, the operating oil pressure of the middle-speedstage clutch C₂ is simultaneously released to the oil tank R andtherefore, the oil pressure within the second pilot oil pressure chamber81' of the timing valve Tv is also released to the oil tank R throughthe oil passage 41₂ '. Thus, the valve body 80 is moved rightwards bythe biasing force of the spring 108. At this time, the timing valve Tvis operated in order of the mode of FIGS. 7C, 7B and 7A from the mode ofFIG. 7D. Thus, even at the change gear time, the modulator pressure Pmis temporarily lowered to release the operation of the direct couplingclutch Cd.

The above-described operation is likewise carried out at the time ofshift-down, wherein the high-speed stage gear train G₃ is shifted to themiddle-speed stage gear train G₂ and the middle-speed stage gear trainG₂ is shifted to the low-speed stage gear train G₁. In either case,connection and interruption of the middle-speed stage clutch C₂ aredetected whereby the timing valve Tv is operated and the direct couplingclutch Cd is temporarily released.

According to this embodiment, in the timing valve Tv, only the modulatorpressure Pm is lowered without connecting the operating oil pressure ofthe low-speed stage clutch C₁ with the oil passage 104 in communicationwith the oil tank R, to release the engagement of the direct couplingclutch Cd. Therefore, it is not feared that the operating oil pressureof the low-speed stage clutch C₁ is excessively lowered with the resultthat the clutch C₁ slips to shorten the service life.

FIG. 9 shows a fourth embodiment of the present invention. Thisembodiment is different from that of FIG. 6 in the control device Dc andin a source of the operating oil pressure of the direct coupling clutchCd, the source being the discharge side of the oil pressure pump P, thatis, the line pressure Pl. However, the operation therefor is almost thesame and therefore, parts in FIG. 9 corresponding to those of FIG. 6 aregiven the same reference characters.

The control device Dc has a modulator valve Mv for generating a variablemodulator pressure Pm by the governor pressure Pg guided through the oilpassage 47₁ ', similar to the embodiment of FIG. 6, and the timing valveTv is connected at the downstream side of the modulator valve Mv. An oilpassage 104 branched from an output oil passage 91 of the modulatorvalve Mv and connected to the oil tank R is opened and closed by thetiming valve Tv. The valve body 80 of the timing valve Tv is moved fromthe first switching position to the lower second switching position asshown by the operating oil pressure of the middle-speed stage clutch C₂.The valve body 80 closes the oil passage 104 at the first switchingposition and second switching position. That is, when the operating oilpressure of the middle-speed stage clutch C₂ is the maximum and zero,namely, atmospheric pressure, the oil passage 104 is closed to transmitthe output oil pressure of the modulator valve Mv to the direct couplingclutch Cd. However, in the halfway or transit stage, the oil passage 104is opened to connect the oil pressure cylinder 14 of the direct couplingclutch Cd with the oil tank R to release the operation thereof. Athrottle 108 is provided at an upstream from the branched point of theoil passage 104 in order to sufficiently reduce the pressure within theoil pressure cylinder 14.

In this embodiment, even when the manual valve Vm is shifted to themiddle-speed stage retaining position II, the oil passage 46 (see FIG.6) is pressurized to generate the governor pressure Pg, and therefore,the direct coupling clutch Cd can be actuated.

FIG. 10 shows a fifth embodiment of the present invention. Also in thisembodiment, the line pressure Pl is used as an oil pressure sourcesimilarly to the embodiment of FIG. 9.

A spool valve body 111 of the modulator valve Mv is biased towards theopen side as shown by means of a spring 112 and biased toward the rightopen side by the oil pressure of the output oil passage 113. A part ofthe output oil pressure is guided also to the oil pressure chamber 114.This oil pressure chamber 114 is connected to the oil tank R through theoil passage 115 which is in turn opened and closed by a pilot vlave 107driven by a solenoid 116. The pilot valve 117 is always biased by aspring 118 and normally closes the oil passage 115. However, when thesolenoid 116 is excited, the oil passage 115 is opened to release theoil pressure chamber 114 to the oil tank R. Thus, when the solenoid 116is deenergized, the oil pressure applied to the valve body 111 of themodulator valve Mv is equal to each other on both sides thereof and thevalve body 111 remains positioned as shown by the force of the spring112. Therefore, the line pressure Pl is released to the oil passage 113but when the solenoid 116 is excited, the valve body 111 is movedrightwards and a fixed pressure lower than the line pressure Pldetermined by the strength of the spring 112 is released to the oilpassage 113.

A lock-up release valve Rv is connected to the output oil passage 113 ofthe modulator valve Mv. A spool valve body 119 of the lock-up releasevalve Rv is biased rightwards by a spring 120. The oil pressure of theoil passage 113 is guided through a throttle 122 to an oil pressurechamber 121 on the right side of the lick-up release valve Rv. This oilpressure chamber 121 is connected to the oil tank R through an oilpassage 123 which is in turn opened and closed by a pilot valve 124. Thepilot valve 124 is driven by a solenoid 125, and when the solenoid 125is deenergized, the oil passage 123 is closed by a spring 126 but whenthe solenoid 125 is excited, the oil passage 123 is opened. Thus, whenthe solenoid 125 is deenergized, the valve body 119 assumes a positionshown leftwardly by the pressure oil supplied to the oil pressurechamber 121 through the throttle 122 to connect the oil passage 113 tothe output passage 127 to guide the oil pressure of the oil passage 123to the oil pressure cylinder 14 of the direct coupling clutch Cd. Whenthe solenoid 125 is excited, the oil pressure chamber 121 is open to theoil tank R, and the valve body 119 is moved rightwards by the force ofthe spring 120 to place the oil passage 127 in communication with theoil tank R to release the operation of the direct coupling clutch Cd.

These two solenoids 116 and 125 are excited or deenergized by anelectronic circuit 128. This electronic circuit 128 control thesolenoids 116, 125 in response to signals from a vehicle speed detector129 and an engine load detector 130. For example, the solenoid 116 isturned On when the vehicle speed is for example below 60 Km/h and turnedON when it is above 60 Km/h. The solenoid 125 is turned ON when theengine is in the idle condition and turned OFF when the engine is in theother conditions, or said solenoid is turned ON when the vehicle speedis for example below 20 Km/h and turned OFF when the vehicle speed isabove 20 Km/h. In this manner, until the vehicle speed reaches 20 Km/hafter the vehicle started, the direct coupling clutch Cd is released bythe function of the solenoid 125 and the function of the torqueconverter T can be utilized. At the vehicle speed lower than 60 Km/h,even if the direct coupling clutch Cd is actuated, the engaging forcethereof is weak. When the throttle pedal is trod, a relative motionoccurs between the pump vane wheel 2 of the torque converter T and theturbine vane wheel 3 even during the operation of the direct couplingclutch Cd. There assumes the power divisional operation wherein a partof power is transmitted even through the torque converter T.

The pressure oil within the pilot oil pressure chamber 121 of therelease valve Rv is discharged to the oil tank R by the excitement ofthe solenoid 125 as described above and at the same time, a part of theoil pressure is discharged at a certain time during the change gearoperation even by the timing valve Tv provided parallel to the releasevalve Rv. The construction and operation of the timing valve Tv are thesame as those shown in FIG. 9 and therefore the explanation thereof willbe omitted. If the pressure oil within the pilot oil pressure chamber121 is discharged, the operation of the direct coupling clutch Cd isreleased and therefore the intended object can be achieved.

In accordance with this embodiment, since the direct coupling clutch Cdof the torque converter T can be actuated irrespective of the shiftposition of the manual valve Vm, the torque converter T can be locked upin three ranges, namely, the drive position D, middle-speed retainingposition II and backward-movement position Re.

Futhermore, in accordance with this embodiment, the timing valve Tv isused as the pilot valve, and the operating oil is circulated by therelease valve Rv from the oil pressure cylinder 14 of the directcoupling clutch Cd to the oil tank R. Therefore, despite the fact thatthe timing valve Tv itself is simple as in the embodiment shown in FIG.9, the engagement and release of the direct coupling clutch Cd can becarried out more accurately.

As described above, in the present invention, the direct coupling clutchis actuated by the signal pressure increased or reduced by the selectionof either gear train and the oil pressure source for generating oilpressure in common even if either gear train is selected, and when thesignal pressure varies, the operation of the direct coupling clutch isreleased. For example, if an arrangement is made so as to detect andcontrol the operating oil pressure of the middle-speed stage clutch, therelease of coupling and re-coupling of the direct coupling clutch can beeffected efficiently at the time of two change gear modes, that is, thelow-speed stage to middle-speed stage and the middle-speed stage tohigh-speed stage. A single timing valve or the like used will suffice,and therefore, the construction of the device is simple and the relianceis high. In addition, since the locking-up of the torque converter overthree adjacent speed ratios may be achieved, fuel cost can be materiallyimproved. Even in the automatic transmission with four stages offorward, if the locking-up is made with three stages, the second, thirdand top, the fuel cost equal to that of the gear transmission can beexpected.

FIG. 12 shows a sixth embodiment of the present invention. Thisembodiment is different from the previous embodiment in the controldevice Dc. This control device Dc comprises a timing valve Tv, amodulator valve Mv and an ON/OFF valve Vo which are hydraulicallyconnected in series. Here, the order of connection of these valves isnot limited to the illustrated order but other orders may be employed.

The timing valve Tv is provided to temporarily release the lock-upcondition of the direct coupling clutch Cd at the time of change gearand comprises a spool valve body 285 which is moved between a rightfirst switching position and a left second switching position, a pilotoil pressure chamber 286 to which a left end surface of the valve body285 faces, a second pilot oil pressure chamber 287 to which a right endsurface of the valve body 285 faces, and a spring 288 for biasing thevalve body 285 rightwards, wherein an oil passage 41₂ ' branched fromthe operating oil passage 41₂ of the middle-speed stage clutch C₂ isconnected to the second pilot oil pressure chamber 287, and the firstpilot oil pressure chamber 286 is communicated with the oil tank Rthrough an oil passage 290. The valve body 285 is provided in the outercircumference thereof with two symmetrical left and right annulargrooves 292, 293 with a land 291 sandwiched therebetween. When the valvebody 285 is in the first switching position as shown, the oil passage41₁ ' branched from the operating oil passage 41₁ to the low-speed stageclutch C₁ is communicated with an output oil passage 294 to themodulator valve Mv. This condition remains unchanged even when the valvebody 285 is in the left second switching position but in the positionhalfway wherein the valve body 285 is moved between the first switchingposition and the second switching position, the output oil passage 294is temporarily shut off from the oil passage 41₁ ' and is communicatedwith only the oil passage 283 branched from the lubricating oil passage38.

For example, in the event that the valve body 285 is moved from thefirst switching position to the second switching position as shown, theoil passage 41' is first closed by the land 291, the oil passage 283 isthen communicated with the output oil passage 294 and the output oilpassage 294 is closed passing through the land 291. Then, the output oilpassage 294 is again communicated with the oil passage 41₁ '.Conversely, in the event that the valve body 285 is moved rightwardsfrom the second switching position to the first switching position, theland 291 first closes the output oil passage 294, the output oil passage284 is then communicated with the oil passage 283, the oil passage 283is closed and finally the output oil passage 294 is communicated withthe oil passage 41₁ '.

When the valve body 285 is in the position as shown, the oil passage 285is communicated with the oil tank R through the first pilot oil pressurechamber 286 but the valve body 285 is moved leftwards during theengagement of the middle-speed stage clutch C₂ and communicated with theoil passage 283 but shut off from the oil tank R.

The modulator valve Mv is provided to form the lock-up engaging forcewith the governor pressure Pg serving as a base and comprises a spoolvalve body 296 which is moved between a right closed postion and a leftopen position, a spring 297 for biasing the valve body 296 towards theopen position, a first pilot oil pressure chamber 298 to which a leftend surface of the valve body 296 faces, a second pilot oil pressurechamber 299 to which a right end surface of the valve body 296 faces, aninput port 300 and an output port 301. The input 300 is connected to theoutput oil passage 294 of the timing valve Tv, and the output port 301is connected to the oil passage 302. The first pilot oil pressurechamber 298 is always communciated with the output port 301 through athrottle 103 provided on the valve body 296.

The second pilot oil pressure chamber 299 is connected through ahigh-select valve Vs to the oil passage 295 and to the oil passage 47₁ 'branched from the first signal oil passage 47₁ which guides the governorpressure Pg. The high-select valve Vs is constructed such that aspherical valve body 326 is housed within a casing 325 whichconcentrically connects the oil passage 295 and oil passage 47₁ '. Thehigh-select valve Vs compares the oil pressure of the oil passage 295,namely, the lubricating oil pressure Pu or zero (atmospheric pressure)with the oil pressure of the oil passage 47₁ ', namely, the governorpressure Pg, and the higher pressure among them is introduced into thesecond pilot oil pressure chamber 299 of the modulator valve Mv.

The ON/OFF valve Vo is provided to release the lock-up of the directcoupling clutch Cd when the opening degree of throttle is in the idleposition and comprises a spool valve body 305 which is moved between aright closed position, that is, a lock-up release position and a leftopen position, a spring 306 for biasing the valve body 305 towards theclosed side, a first pilot oil pressure chamber 307 to which a left endsurface of the valve body 305 faces, and a second pilot oil pressurechamber 308 to which a right end surface of the valve body 305 faces.The input port is communicated with the oil passage 302 from themodulator valve Mv, and the output port is communicated with theinterior of the oil pressure cylinder of the direct coupling clutch Cdthrough an output oil passage 309. The second pilot oil pressure chamber308 is connected to an oil passage 310 branched from the oil passage 282which guides oil pressure proportional to the opening degree of thethrottle of the engine E to back-pressure chambers of the accumulators72 and 73 from the valve Vt', and the first pilot oil pressure chamber307 is connected to the oil tank R.

The ON/OFF valve Vo is opened when the output of the valve Vt', that is,the oil pressure proportional to the opening degree of the throttle ofthe engine E overcomes the spring force of the spring 306 to guide theoutput of the modulator valve Mv to the oil pressure cylinder 14 of thedirect coupling clutch Cd. When the output of the valve Vt' is smallerthan the spring force of the spring 306, the valve opens to bring theoil passage 309 into communication with a release port 311, and the oilpressure within the oil pressure cylinder 14 is released to the oil tankR.

While the oil pressure from the valve Vt' provided to alleviate theshock at the time of change gear is exerted on the second pilot oilpressure chamber 308, it is noted that in principle, the throttlepressure Pt from the throttle valve Vt can be exerted thereon.

Next, the operation of this embodiment will be explained. The lock-upcontrol of the direct coupling cluch Cd is effected only when the manualvalve Vm is in the drive position D and therefore, only this case willbe explained.

First, when the vehicle is started with the manual valve Vm shifted tothe drive position D, the oil pressure is not exerted on the oil passage41₂ ' because the change gear ratio is initially in the low-speed stage,and thus the timing valve Tv is in the first switching position shown inFIG. 12. The oil pressure of the oil passage 295 is zero, and thegovernor pressure Pg from the oil passage 47₁ ' is exerted on the secondpilot oil pressure chamber 299 of the modulator valve Mv from thehigh-select valve Vs.

At that time, in the modulator valve Mv, the oil pressure of the outputport 301 is exerted on the first pilot oil pressure chamber 298 throughthe throttle 303, and said oil pressure imparts the rightwardly movingforce to the valve body 296. When this rightwardly moving forceovercomes the leftwardly moving force for the valve body 296 resultingfrom the spring 297 and the governor pressure Pg introduced into thesecond pilot oil pressure chamber 299, the valve body 296 is movedrightwards so as to close the input port 300. When the relation of theforces therebetween is reversed, the valve body 296 is operated so as toopen the input port 300. As a consequence, the output oil pressure ofthe output port 301, that is, the operating oil pressure of the directcoupling clutch Cd is increased to a fixed level from the governorpressure Pg proportional to the vehicle and is as shown by the curve αin FIG. 13. When the operating oil pressure reaches the vehicle speed Aabove the internal pressure Pc of the torque converter T, the piston 13of the direct coupling clutch Cd is moved rightwards at a speed abovesaid vehicle speed, the direct coupling clutch Cd is engaged and thetorque converter T is locked up.

When the vehicle speed further increases to establish the change gearratio of the middle-speed stage, the timing valve Tv is moved leftwardsto assume the second switching position and the oil passage 295 iscommunicated with the oil passage 283. Therefore, the oil pressureguided from the high-select valve Vs to the second pilot oil pressurechamber 299 of the modulator valve Mv is a higher one among the governorpressure Pg or lubricating oil pressure Pu, and the oil pressureresulting from the increase in such higher oil pressure is the outputoil pressure of the modulaor valve Mv, that is, the operating oilpressure of the direct coupling clutch Cd. The magnitude of thelubricating oil pressure Pu can be selected as shown in FIG. 13 tothereby make the aforesaid operating oil pressure higher than theinternal pressure Pc of the torque converter T as shown in the curve β,and the direct coupling cluch Cd can be locked up at a speed lower thanthe vehicle speed A, In FIG. 13, a slightly right and upward indicationof the lubricating oil pressure Pu results from the phenomen wherein thequantity of surplus oil increases with the increase in vehicle speed,that is, with the increase in the number of revolutions of the engine E,but it can be considered to be approximately horizontal.

In case of the change gear ratio of the high-speed stage, it is limitedthat the lock-up operation of the direct coupling clutch Cd is effectedat a speed above the vehicle speed A, but there practically poses noproblem as shown in FIG. 14. That is, in FIG. 14 showing the typicalcharacteristic map of the hydraulic automatic transmission, three zonesI, II and III defined by the dotted lines designate the low-speed zone,middle-speed zone and high-speed zone, respectively. Since the zone IIIof the high-speed zone is limited to the speed above the vehicle speed,there is no actual harm. On the other hand, in the middle-speed zone II,the lock-up operation can be made in its whole zone, and the actual fuelcost is improved. While it is obvious if one assumes the time thevehicle is stopped, when the shift-down is made to the low-speed stage,the lock-up condition is released at a speed below the vehicle speed A.Thus, the possibility of the engine stop can be avoided without using aspecial switching valve which performs the switching operation inresponse to the vehicle speed. The horizontal line indicated by thesolid lines in FIG. 14 designates the lock-up release line by the actionof the ON/OFF valve Vo.

While in this embodiment, the switching of the action of the lubricatingoil pressure Pu to the oil passage 295 has been performed by the timingvalve Tv, an exclusive-use switching valve for the purpose of suchswitching can be provided separately from the timing valve Tv. Inaddition, while the governor pressure Pg and lubricating oil pressure Puhave been introduced into the high-select valve Vs, oil pressure fromanother oil pressure generating means for generating a substantiallyfixed oil pressure in response to the operation of the engine E, inplace of the lubricating oil pressure Pu, can be introduced into thehigh-select valve Vs.

FIG. 15 shows another structure of the timing valve. In this timingvalve Tv, between a port 283a to which is connected the oil passage 283and a port 294a to which is connected the oil passage 294 is provided afurther port 328 which is in turn communicated with the oil tank R.According to this embodiment, when the valve body 285 is movedrightwards to assume the first switching position, the oil passage 295is communicated with the oil tank R through the port 328, and the oilpressure of the oil passage 295 is zero. While the function similar tothe timing valve Tv in FIG. 12 can be performed even by the timing valveTv, the timing valve Tv in FIG. 12 can be constructed to be more compactthan the other. In the timing valve Tv in FIG. 12, the description hasbeen made such that when the valve body 285 is moved between the firstswitching position and the second switching position, the oil passage283 is temporarily communicated with the output oil passage 294 torelease the lock-up, but this is limited to the case where thelubricating oil pressure Pu is lower than the internal pressure Pc ofthe torque converter T. Otherwise, a port 328 in communication with theoil tank R need be provided as in the timing valve Tv in FIG. 15.

The oil passage 41₁ ' branched from the oil passage 41₁ for supplyingthe operating oil to the low-speed stage clutch C1 is connected to thetiming valve Tv in FIGS. 12 and 15 because the lock-up of the torqueconverter T is effected only at the drive position D, and in order thatsaid lock-up is effected at the middle-speed retaining position II, theoil passage branched from the oil passage 43 can be connected thereto.While the aforesaid timing valve Tv is made to have the switchingfunction of the lubricating oil pressure Pu, it will be noted that anexclusive-use switching valve for switching the lubricating oil pressurecan be provided separately from these timing valves Tv.

FIG. 16 shows an embodiment in which the lock-up of the torque converterT is effected only at the time of change gear ratios of the middle-speedstage and high-speed stage. A timing valve Tv is interposed between theoil passage 41₂ ' branched from the oil passage 41₂ (see FIG. 12) forsupplying the operating oil to the manual valve Mv and middle-speedstage clutch C₂ and the oil passage 41₃ ' branched from the oil passage41₃ for supplying the operating oil to the high-speed stage clutch C₃.This timing valve Tv comprises a spool valve body 331 which is movedbetween a left first switching position and a right second switchingposition, a first pilot oil pressure chamber 332 to which a left endsurface of the valve body 331 faces, and a second pilot oil pressurechamber to which a right end surface of the valve body 331 faces,wherein the first pilot oil pressure chamber 332 is communicated withthe oil passage 41₃ ' through a throttle 334, and the second pilot oilpressure chamber 333 is communicated with the oil passage 41₂ ' througha throttle 335. Thus, when the change gear ratio of the middle-speedstage is established, the valve body 331 is in the left first switchingposition and the oil passage 41₂ ' is communicated with the output oilpassage 294. When the change gear ratio of the high-speed stage isestablished, the valve body 331 is in the right second switchingposition, and the oil passage 41₃ ' is communicated with the output oilpassage 294. Since the lock-up is not effected at the low-speed stage,the oil passage 283 for guiding the lubricating oil pressure Pu isdirectly connected to the high-select valve Vs. According to thisembodiment, when the change gear ratios of the middle-speed stage andhigh-speed stage are established, torque converter T is locked up, andtherefore, this mode is distinguished from the embodiment in connectionwith FIG. 14 in which the torque converter T is not locked up at a speedbelow the vehicle speed A.

FIG. 17 shows an embodiment in which the lubricating oil pressure Pu isso high that the lock-up may be effected only by itself. In thisembodiment, it is not necessary to increase the lubricating oil pressurePu by the modulator valve Mv. Therefore, the high-select valve Vs isarranged so that the oil pressure of the ouput oil passage 302 from themodulator valve Mv is compared with the oil pressure of the oil passage283 for guiding the lubricating oil pressure Pu, and the higher oilpressure resulting therefrom is guided to the ON/OFF valve Vo.

FIG. 18 shows an embodiment in which the operation release of the torqueconverter T are controlled in response to the vehicle speed. A secondpilot oil pressure chamber 308 on the ON/OFF valve Vo is connected tothe oil tank R through the switching valve Vc. This switching valve Vccomprises a spool valve body 340 which is moved between a left closedposition and a right open position, a spring 341 for biasing the valvebody 340 towards the open side, a first pilot oil pressure chamber 342to which a left end surface of the valve body 340 faces, and a secondpilot oil pressure chamber 343 to which a right end surface of the valvebody 340 faces. An oil passage 344 branched from an oil passage 310 forguiding the oil pressure proportional to the opening degree of thethrottle of the engine E to the second pilot oil pressure chamber 308 ofthe ON/OFF valve Vo is connected to the first pilot oil pressure chamber342, and an oil passage 345 branched from the oil passage 47₁ ' forguiding the governor pressure Pg is connected to the second pilot oilpressure chamber 343. The second pilot oil pressure chamber 308 of theON/OFF valve Vo is connected to an input port 346 through an oil passage347, and an output port 348 is connected to the oil tank R.

In accordance with this embodiment, when the vehicle speed lowers, thevalve body 340 is moved rightwards to bring the input port 346 intocommunication with the output port 348, the oil pressure within thesecond pilot oil pressure chamber 308 is released to the oil tank R toclose the ON/OFF valve Vo, and the oil pressure within the cylinder 14in the direct coupling clutch Cd is released to the oil tank.Accordingly, the lock-up condition of the torque converter T is forciblyreleased at the time of lowering of the vehicle speed, and therefore,the lock-up zone in the low-speed stage can be enlarged towards thelower speed side.

While in any of the above-described embodiments, the description hasbeen made of the automatic transmission of three stages of forward, itwill be noted that in the automatic transmission of four stages offorward, the torque converter T can be locked up at each of change gearstages, namely, the second, third and top. In that case, it is necessaryto use an oil pressure source which can be increased at each of changegear stages, namely, the second, third and top but cannot be increasedat the change gear stage of low gear. Such an oil pressure source usedis the oil pressure of the output oil passage 70 of the low-middle speedshift valve V₁.

While in the foregoing, the clutches C₁, C₂ and C₃ are increased inpressure to establish the gear trains G₁, G₂ and G₃, respectively, itwill be noted that in case of using brake bands, the clutches arereduced in pressure to establish the gear trains G₁, G₂ and G₃,respectively. It will be apparent that even in such a case as justmentioned, movement of the aforesaid timing valve Tv is merely reversedand the similar operation is obtained.

Moreover, while in the above-described embodiments, the direct couplingclutch Cd used was of the the roller type, it is noted that other typesof the direct coupling clutch can be used. For example, the directcoupling clutch includes one which is the disk type with a facingmaterial adhered thereto, which receives the internal pressure of thetorque converter T to couple the input and output members. This can beeasily applied by an arrangement wherein for example, a timing valve isused as a pilot valve and an original control valve is shifted to aninoperative position.

As described above, in the present invention, there are provided an oilpressure generating means for generating oil pressure of a fixed levelin response to the operation of the engine and a selection means forcomparing the governor pressure from the governor valve with the oilpressure generated by said oil pressure generating means to select andrelease a higher oil pressure among them, and the output of theselection means is used as an index for controlling the engaging forceof the direct coupling clutch. Therefore, even during the running at thechange gear ratio of the low-speed stage, the engaging oil pressurenecessary for locking up the torque converter can be secured and theproblem of vibrations in the middle-speed zone can be solved toconsiderably improve the practical fuel cost. Furthermore, if aswitching valve is provided to switch a supply of the operating oilpressure to the direct coupling clutch, the zone that may lock up thetorque converter is extended to a lower speed zone. Yet, since thedirect coupling clutch is of the power divisional type, even if thetorque converter is locked up in the low-speed zone, it is not fearedthat the performacne of power is deteriorated and the vibration of thevehicle body is increased. As a result, the governor pressure can be setso as to have the characteristic most suitable for the change gear toincrease the freedom of design.

Moreover, a control means for interrupting between a selecting means andan oil pressure generating means when the gear change ratio of thelow-speed stage is established is interposed between the selecting meansand the oil pressure generating means. Therefore, the characteristicwherein the governor pressure is rapidly lowered in response to thelowering of the vehicle speed can be utilized to release the lock-upcondition of the torque converter in the change gear ratio of thelow-speed stage. accordingly, it is possible to extend the lock-up zoneto the lower speed zone without occurrence of the engine stop in thelow-speed zone, without provision of an exclusive-use switching valve ofwhich switching mode varies with the vehicle speed, and possible toimprove the practical fuel cost.

What is claimed is:
 1. In the automatic transmission for a vehicle,comprising a fluid type torque converter having an input member and anoutput member; a hydraulic direct coupling clutch provided between theinput and output members and capable of being actuated to mechanicallycouple both members together; and auxiliary transmission connected tothe torque converter and having plural stages of gear trains, theauxiliary transmission being capable of being changed in speed to aplurality of speed ratios by selection of the gear trains; and a controlmechanism for automatically effecting the selection of gear trains ofthe auxiliary transmission in accordance with the running condition ofthe vehicle,a lock-up control device for the direct coupling clutchcomprising: a valve for controlling the supply of actuating oil pressurefrom a common oil pressure source to the direct coupling clutch, saidvalve having a body movable between opposite end position and adapted totake a first switch position at one of said end positions when appliedwith a single signal pressure and a second switch position at the otherof said end positions, after release of the signal pressure, due toresilient force of a spring means, said signal pressure being of such acharacteristic that it becomes high when an intermediate gear train isselected to assume a specific gear ratio and it becomes low when higherand lower gear trains adjacent said intermediate gear train are selectedto assume corresponding gear ratios adjacent said specific gear ratio,and wherein said valve allows flow of the actuating oil pressure to thedirect coupling clutch when the valve body is at both the first andsecond switch positions and interrupts the flow during shifting movementof the valve body from the first to second positions or vice versa inresponse to gear shifting operation from said specific gear ratio to itsadjacent gear ratios or vice versa, thus causing the direct couplingclutch to be instantaneously disconnected during gear shifting operationover adjacent three gear ratios with use of the single signal pressure.2. A control device as defined in claim 1, wherein the signal pressureis an operational oil pressure to be used for engagement of anintermediate stage clutch of an intermediate-speed gear train.
 3. Acontrol device as defined in claim 1, wherein the oil pressure foractuation of the direct coupling clutch is an operational oil pressureto be used for engagement of a low speed clutch of a low speed geartrain.
 4. A control device as defined in claim 1, wherein in an oilpassage connecting an output port of the valve and an input port of thedirect coupling clutch, a modulator valve is interposed which is capableof disconnecting a connection between the input and output ports inresponse to a travelling condition of the vehicle.